The numbers are striking. Seattle's docked system, Pronto, which shut down in January, had fewer than 10,000 rides per month over two and a half years. Dockless Spin, LimeBike and Ofo combined for nearly 58,000 rides per month in their first six months.

To be sure, various differences were factors. But it stands to reason that the lack of docking stations was the primary cause. Riders like the idea of being able to park their bike (and stop paying) anywhere, any time.

Of course, parking anywhere is also a shortcoming of dockless systems because some users leaves bikes in bad spots, such as blocking sidewalks and handicapped ramps, and vandals occasionally move or damage them. In Seattle, some bikes were dumped in Puget Sound or even strung up in trees, as one dockless-system skeptic noted to Crain's.

No system is perfect. Consider motor vehicles: Drivers often double-park or block curb cuts, hydrants, crosswalks and street sweepers. But no one suggests a docking system for cars and trucks.

In New York, Citi Bike has been a success, unlike Seattle's docked system. And it has been entirely privately funded, thanks to the marketing value of Manhattan's central business district and a few other neighborhoods around town where Citi Bike has a presence.

But it is not clear that Citi Bike would be economically viable in the many parts of the city it does not yet serve. And the de Blasio administration neither wants to subsidize Citi Bike's expansion nor grant it exclusivity, given the potential popularity, favorable economics and ease of deployment of dockless systems across the boroughs. That is why the Department of Transportation this month issued a request for expressions of interest from dockless bike-share operators, who see New York City as a huge prize.

Motivate, the company that operates Citi Bike, could itself develop a dockless system for New York. It has to at least explore the possibility, given the chances that its legacy docked system becomes obsolete. (Think of the way soda companies introduced their own brands of sport drinks and bottled water when those beverages began to erode carbonated soft drinks' market share.) But while Motivate is competing with LimeBike to install a dockless system in Minneapolis, it has some catching up to do with dockless companies that are already operating in a handful of U.S. cities as well as overseas.

Crain’s New York Business is the trusted voice of the New York business community—connecting businesses across the five boroughs by providing analysis and opinion on how to navigate New York’s complex business and political landscape.